Carboxylated latex, for example styrene-butadiene-itaconic acid terpolymers, have been prepared by a variety of methods. For example, U.S. Pat. No. 4,480,078 discloses a continuous emulsion polymerization process for producing carboxylated styrene-butadiene latices characterized in that only a portion of the primary monomers are charged to the first reaction zone followed by subsequent injection of the remaining portion of the primary monomers to the following reaction zone in an overall process using two or more reactors. According to this method, a portion of the conjugated diene and the non-carboxylic acid monomer are added to the first reaction zone with the remaining portion of each primary monomer being charged thereafter. Unfortunately, this method still contributes to the formation of 4-phenylcyclohexene (4-PCH).
U.S. Pat. No. 3,969,432 relates to a process of copolymerizing a vinyl aromatic monomer with from about 0.5 to about 6 percent of a conjugated diene monomer based on the total weight of the monomers. Initially the vinyl aromatic monomer is copolymerized by a free radical mechanism with about 15 to about 70 percent by weight of the total quantity of the conjugated diene monomer. Thereafter, the remainder of the conjugated diene, 85 to 30 percent by weight, is added to the copolymerization system and the polymerization reaction is continued. Unfortunately, the undesirable characteristic of this process is that the Diels-Alder reaction can take place to form 4-PCH in large amounts.